The prior art discloses numerous devices for stopping or metering the flow of granular materials. Typical of these are slide gates, rotary vane gates, quadrant gates, butterfly valves and so forth. Illustrative of the prior art are U.S. Pat. Nos. 2,885,129; 2,917,208 and 2,919,158.
Each of the prior art designs has one or more of the following deficiencies: Valve seats, seals or tight clearances between moving parts cause seizing, binding or galling, premature wear and require excessive force or torque to operate. Housings permit contamination from the surrounding atmosphere, allow internal pressure and material to leak out or allow rain water or other contamination to enter. Vanes, blades or plates enable the material to become caught between two opposing edges during the final closing which requires the particles to be sheared or crushed. This causes premature wear or damage to the parts and may prevent complete closing. The closing movement lifts, lowers or compacts material. The valve contains pockets such that the gate is not completely drainable or self-cleaning. Valves must be installed at an angle or in a fashion that prevents the inlet port and outlet port from having a common center line.
It is desirable to have available a gate that not only eliminates all of the above deficiencies, but is also simple and inexpensive to construct.